The present invention generally relates to phase shift masks and more particularly to an improved phase shift mask that uses liquid phase deposition oxide as a phase shift material.
As optical lithography is extended to images substantially smaller than the exposure wavelength, the use of resolution enhancement techniques is needed, such as altering (alternating) phase shift. The fabrication of altering phase shift masks is limited by the uniformity capabilities of the etch processes that define the phase shift regions. The etch processes do not have an etch stop layer, so the inherent pattern factor and across substrate variations in the RIE chamber are replicated in the substrate. This variation in etch depth causes a small focus window and an effectively reduced resolution. The invention described below addresses these issues.